High-speed, low-power optical modulation apparatus and method

ABSTRACT

A gap in an optical guideway is occupied, when the switch is in its diverting condition, by a quantity of air or other gas. To change the switch to its through condition, an actuator forces a column of liquid against the gas to compress (and thereby displace) the gas in the gap with the liquid. The actuator includes a preferably wide reservoir of the liquid and a diaphragm which is flexed to force the liquid up the column against the gas. When the actuator is deactivated the compressed gas forces the column of liquid out of the gap to return the switch to the diverting condition.

[0001] This document is based in part upon, and claims priority from,provisional applications No. 60/289,883 and No. 60/327,760 of DavidKane; and No. 60/327,759 of David Kane and Nichol McGruer. All three arewholly incorporated by reference into the present document.

BACKGROUND

[0002] 1. Field of the Invention

[0003] This invention relates generally to modulation of opticalcircuits and networks; and more particularly to method and apparatusproviding faster switching or modulation speed with lower power thanheretofore available.

[0004] 2. Related Art

[0005] A seminal effort in this field is U.S. Pat. No. 4,988,157 ofJackel—assigned to Bell Communication. That patent teaches use of achemically (to be more specific, electrolytically) creatable anddestroyable bubble, and its implications on total internal reflection,for optical modulation.

[0006] U.S. Pat. Nos. 5,699,462 and 5,960,131 of Fouquet et al., andU.S. Pat. No. 5,978,527 of Donald, represent applications of thethermal-inkjet technology refinements of Hewlett Packard Company tolight modulation or switching. Though faster than electrolysis, thermaleffects operate on the order of milliseconds and accordingly are farfrom optimal in switching speed.

[0007] U.S. Pat. No. 5,619,600 of Pohl and U.S. Pat. No. 5,774,252 ofLin et al. represent entries in somewhat related fields on behalf of IBMand Texas Instruments, respectively; and Japanese publication 5-49055 of1993 represents a related effort by Nippon Telegraph & TelephoneCorporation. Pohl teaches tunneling of light through liquid metal, forpathlengths on the order of a fractional wavelength; possibly useful forkilohertz CW modulation, this technique too is relatively slow forswitching.

[0008] As can now be seen, the related art remains subject tosignificant problems. The efforts outlined above—althoughpraiseworthy—leave room for considerable refinement.

SUMMARY OF THE DISCLOSURE

[0009] The present invention introduces such refinement. In preferredembodiments of a first of its independent aspects or facets, theinvention is an optical-modulation method.

[0010] It includes the step of moving exactly one liquid-gas interface,through compression or expansion of a gas bubble by the liquid. It alsoincludes the step of using the position of the interface to controllight transmission along a light path.

[0011] In a second of its independent facets or aspects, the inventionis an optical-modulation method. It includes the step of compression orexpansion, by a liquid, of a preexisting bubble of gas of a substancedifferent from the liquid. It also includes the step of usingrelationships between properties of the liquid and the gas to controllight transmission along a light path.

[0012] In preferred embodiments of its third major independent facet oraspect, the invention is an optical modulation apparatus that includesan exclusively mechanical transducer for displacing a volume of liquidas between at least two positions. It also includes an at leastpartially mechanical actuator for operating the transducer.

[0013] The apparatus also includes an optical transmission path thatintersects the liquid volume when the volume is in one of the positions,and that does not intersect the volume when the volume is in another ofthe positions.

[0014] In preferred embodiments of its fourth major independent facet oraspect, the invention is optical modulation apparatus. It includes afluidic transducer having stroke amplification through a ratio ofcross-sections between driving and driven stages.

[0015] It also includes a variable-reflection optical cell having acontrol liquid displaced by the driven stage of the transducer. Inaddition, the apparatus includes an optical transmission path modulatedby the cell

[0016] All of the operational principles and advantages of the presentinvention will be more fully appreciated upon consideration of thefollowing detailed description, with reference to the appended drawings,of which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a two-part diagram of a fluidic actuator-strokeamplifier used in preferred embodiments of the invention, the uppersection of the diagram being in plan, and the lower in elevationalcross-section—and showing the actuator relaxed so that the liquid levelis relatively low;

[0018]FIG. 2 is another elevational cross-section like the bottom partof FIG. 1, but with the actuator extended to push the diaphragm andthereby liquid upward, expelling some fluid from the reservoir into thewell;

[0019]FIG. 3 is a multipart diagram showing at left a buried-channelwaveguide-array grid, at upper right two plan views of one individualwaveguide of the array—with the “FASA” in the left-hand one of those twoviews set for total internal reflection (“TIR”), and in the right-handone of those two views set for transmission by virtue of an operational(i.e. imperfect) index match of fluid in the well with the material ofthe optic fiber or other waveguide proper—and at lower right twocorresponding elevational cross-sections as before (i.e. the left-handone showing the transducer and diaphragm set for TIR; and the right-handone, for transmission);

[0020]FIG. 4 is a set of comparative illustrations and relatedcross-references summarizing the general state of the art;

[0021]FIG. 5 is a pair of diagrams like FIG. 1, but for a differentapplication of the FASA—namely, placement of a chemical or biologicalspecimen into an analytical light beam;

[0022]FIG. 6 is a diagram analogous to FIG. 2 but for the FIG. 5application;

[0023]FIG. 7 is a plan view of an analogous configuration for achip-based waveguide in a chemical or biological sensor—in this case,the FASA being used to direct material into one or another differentdetection channel;

[0024]FIG. 8 is a conceptual diagram suggesting disposition of a largemultiplicity of such sensors on a single chip;

[0025]FIG. 9 is a pair of cross-sectional elevations analogous to FIGS.2, 6 etc. but showing expulsion or acquisition of the specimen by thewell of the FASA;

[0026]FIG. 10 is a triad of photographs, the first showing an oversize(250:1 scale) acrylic and polycarbonate prototype of a μFASA—i.e. whatmay be called a “milliFASA” or “mFASA”—and the second and third showingan actual demonstration of successful operation, with light reflectedand transmitted, respectively, at the junction;

[0027]FIG. 11 is an elevational cross-section, somewhat conceptual, of aμFASA (and very nearly the mFASA prototype) assembly, essentially anassembly drawing and with parts numbered for keying to many of thefollowing drawings;

[0028]FIG. 12 is a corresponding plan view of the FIG. 11 top-levelassembly;

[0029]FIG. 13 is a plan of the waveguide layer 3 in FIG. 11, and atright a highly enlarged inset view of the intersection detail;

[0030]FIG. 14 is an elevation view of the FIG. 13 waveguide layer;

[0031]FIG. 15 is a plan with associated elevation, partly in section, ofthe top cap 1 in FIG. 11;

[0032]FIG. 16 is a like drawing pair but showing instead the top column2 in FIG. 11;

[0033]FIG. 17 is a like pair but for a reservoir 4 in FIG. 11;

[0034]FIG. 18 is a like pair for the membrane 6 in FIG. 11;

[0035]FIG. 19 is a like pair, but with no part in section;

[0036]FIG. 20 is a plan view like the upper views in FIGS. 15 through18, but for the base 5 in FIG. 11;

[0037]FIG. 21 is an elevation, partly in section, like the lower viewsof FIGS. 15 through 18, but for the FIG. 20 base;

[0038]FIG. 22 is an external elevation of the actuator 9 in FIG. 11,with its movable spindle fully retracted;

[0039]FIG. 23 is a like view but with the same spindle fully extended;

[0040]FIG. 24 is a photograph of the piezoelectric stack 8 in FIG. 11,also showing a U.S. dime for scale;

[0041]FIG. 25 is a pair of drawings—elevation and plan viewsrespectively for the FIG. 24 stack;

[0042]FIG. 26 is a like pair of drawings for an actuator shim 12 (notshown in FIG. 11);

[0043]FIG. 27 is an longitudinal section, in elevation, for a septuminjector nut that is used for filling; and

[0044]FIG. 28 is a disc 13 (not shown in FIG. 11).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Some of the preferred embodiments of the invention are discussedin this section; they provide a high-speed, low-energy optical switch.

[0046] A gap in an optical guideway is occupied, when the switch is inits diverting condition, by a quantity of air or other gas. To changethe switch to its through condition, an actuator forces a column ofliquid against the gas to compress (and thereby displace) the gas in thegap with the liquid.

[0047] The actuator includes a preferably wide reservoir of the liquidand a diaphragm which is flexed to force the liquid up the columnagainst the gas. When the actuator is deactivated the compressed gasforces the column of liquid out of the gap to return the switch to thediverting condition.

[0048] Viewed broadly, the prior-art patents disclose optical switcheswhich operate by exchanging gas and liquid in a gap in an opticalguideway. These devices utilize either micro-heaters or electrolyticdevices to alternatively create and dissipate gas bubbles in the gap, orto shift a gas bubble into and out of the gap. Thus the specific meansfor changing the medium in the gap from a gas to a liquid and back aredifferent from those of the present invention, which preferably use anactuator in which a liquid column compresses a gas body to effect thechange.

[0049] As to the actuator itself, prior-art diaphragm-deflection devicestypically are not used to compress a gas body, but rather to ejectmaterial, particularly liquid.

[0050] Thus the present device uses different means to accomplish theswitching, as compared with heaters and electro-optical devices. Thereis no teaching in the prior art of using the types of actuator discussedherein for a similar purpose, i.e. compressing and thereby displacing abody of gas, a preexisting bubble, from a gap in the optical guideway.

[0051] The invention is not limited to specific types of actuator; butthose which are specifically discussed herein particularly includedevices that are essentially mechanical—as distinguished from those thatinvolve chemical reactions (as in an electrolytic system) orthermal-vaporization phenomena (as in an inkjet system). The mechanicaldevice, however, may be driven in any one of a variety of ways and notnecessarily by electrical triggering; for example it might be triggeredby an optical signal—either producing thermal effects or otherwise—andthis would have the benefit of maintaining more nearly an overallall-optical system.

[0052] Another advantageous feature of some actuators specificallydiscussed in this document is use of a single fluid/liquid-gas interfaceat which liquid compresses gas. Release of that pressure restores theinterface position.

[0053] Some others do have at least one interface, but in theelectrolytic case the interface is a transient phenomenon (the bubble isnot preexisting)—and in the thermal case the closest embodiment appearsto have not one but two interfaces, and without significant compression(see e.g., the Fouquet patents mentioned earlier, in which adual-interface bubble of generally constant size is translated into andout from the optical path). In preferred embodiments of the presentinvention, by comparison, there is only one stable interface and onlyits position varies during operation.

[0054] The present invention offers the following advantages overprior-art switches:

[0055] much shorter switching time, namely submicroseconds vs. one ortwo milliseconds;

[0056] much less power consumption—by orders of magnitude; and

[0057] possibly, a higher density of switches—to the extent that theactuators occupy less space than the heaters etc. of the prior art.

[0058] The accompanying drawings are self explanatory and show myriaddetails of a constructed, operative and highly preferred embodiment thathas been actually reduced to practice at the expense of the assignee.

[0059] The “fluid-based actuator stroke-amplification” (FASA) systemprovides a method for the amplification of relatively short-strokeactuators such as piezoelectric, electrostrictive or magnetostrictivedevices. In this implementation, an actuator displaces a diaphragmadjacent to a fluid reservoir by Δx as illustrated in FIG. 2. Theresulting volume of the reservoir is changed by (A_(Res))·(Δx). A wellof cross-sectional area A_(well) is coupled to the reservoir, and thefluid column in the well will travel a distance ΔX that is proportionalto:

ΔX=Δx·(A _(Res) /A _(Well))

[0060] One device that can take advantage of the FASA is an all-opticalcrossconnect system that uniquely “switches” incoming light from fiberoptic channels 1-N into Outgoing Channels 1-M as suggested in FIG. 3. Inthis implementation, a buried waveguide (FIG. 4) is configured in a gridarrangement with horizontal waveguides for incoming light, channels 1-N,and vertical waveguides for channels 1-M.

[0061] At each intersection is a FASA well that is at a 45° angle, witha column perpendicular to the waveguide gridwork as shown. At the baseof each column is the reservoir for the FASA and the forcing actuator.

[0062] When the actuator is relaxed, a gas is present at the waveguideintersection and total internal reflection (TIR) occurs for any lightentering horizontally—which is accordingly reflected vertically asshown, due to the difference in refractive index. When the actuator isextended Δx, the index-matched fluid column relative to the waveguidewill rise by ΔX and transmission through the intersection will result asshown.

[0063] A FASA system is located at each horizontal/vertical waveguideintersection. Through the ability to independently switch each FASA, anoptical switch results.

[0064] Currently there are three technologies used to provideall-optical switches. First is the buried waveguide technology, withindex-matched fluids that either are present or absent at anintersection as shown in FIG. 4.

[0065] Agilent (reference in FIG. 4) is utilizing inkjet technology toaccomplish this task; the FASA system introduced here provides anadvantageous alternative. Lucent and other vendors are proposingfree-space solutions, where MEMS mirrors pop up to “switch” channels.Chronus is proposing a liquid-crystal device for switching.

[0066] Primary advantages of the FASA approach are switching speedfaster by ten to a hundred times, and power consumption approximatelyone tenth.

[0067] A 250:1 scale acrylic/polycarbonate prototype of a singleactuator/fluid column junction with 500:1 stroke amplification has beenbuilt and demonstrated as a reduction to practice of μFASA opticalswitching. A photo of the prototype and imagery of the two switch states(FIG. 10), and assembly diagrams of the apparatus (FIGS. 11 and12)—together with individual component detail drawings (FIGS. 13 through28) document this demonstration of a single mFASA switch.

[0068] With the actuator relaxes (second image of FIG. 1), an air bubbleresides at the waveguide-column interface. As a result, the input laserbeam reflects from the interface at a 90° angle, due to TIR as shown.Because of multimode operation at this scale, some of the laser beampasses through the intersection.

[0069] In the FIG. 2, the actuator 8 is extended—and isopropyl alcoholthat is in the reservoir and column compresses the bubble at the top ofthe column, so that now fluid is at the waveguide/column interface.Under these conditions the light beam can propagate through the regionas shown.

[0070] The actuator (FIGS. 22 and 23) is a product from ThorLabs ofNewton, N.J. It has a movable spindle CL in fully retracted position,and CP in fully extended—with total travel of 250 μm minimum. It has a{fraction (1/4)}-80 external thread CQ (class 3 fit) and coarsetravel-locking nut CR.

[0071] The entire body CS rotates for coarse travel. The fine adjust CTmakes 25 μm per revolution, advancing at 0.5 μm per smallest graduation.The stack 8 actuates finely also.

[0072] The dimensions are: CW 2.08 inch (53 mm), CV 0.15 inch (3.8 mm),CU diameter 0.69 inch (17.6 mm), CM 0.86 inch (22 mm), CH 1.88 inch (47mm), CO 0.13 inch (3.3 mm).

[0073] A second application of the FASA is as a micropump, used to drawand expel chemical or biological molecules into the well, in a regionwhere light from a waveguide interacts with the molecule (FIGS. 5 and6). In this configuration, the wall of the well is perpendicular to thewaveguide and light is transmitted through the well as shown.

[0074] The intent is to identify the molecule by unique signaturesassociated with fluorescence, index or polarization variation, orcombinations of these. In all configurations, a reference leg closed tothe atmosphere provides the baseline signal, and this is compared to theopen well where the molecule interacts with the light traveling throughthe buried waveguide—based on detector output (FIGS. 7 and 8). Herethere are a relative intensity comparison in the first configuration,and an interferometer imbalance due to phase change as a result ofvarying index in the second.

[0075] It will be understood that the foregoing disclosure is intendedto be merely exemplary, and not to limit the scope of theinvention—which is to be determined by reference to the appended claims.

What is claimed is:
 1. An optical-modulation method comprising the stepsof: moving exactly one liquid-gas interface, through manipulation of agas bubble by the liquid; and using the position of the interface tocontrol light transmission along a light path.
 2. The method of claim 1,wherein: the using step comprises controlling the transmission byvariation of reflection at a chamber containing the bubble and liquid.3. The method of claim 2, wherein the chamber is interposed along thepath; and: the reflection is used to control transmission across thechamber.
 4. The method of claim 2, wherein the variation comprisesshifting between: substantially total reflection; and a smaller amountof reflection.
 5. The method of claim 4, wherein: the smaller amount ofreflection is a substantially unavoidable level of reflection for theliquid and a material of the chamber.
 6. The method of claim 2, wherein:the moving step comprises mechanically displacing a volume of theliquid.
 7. The method of claim 6, wherein: the displacing step comprisesshifting a diaphragm in contact with the liquid.
 8. The method of claim7, wherein: the shifting step comprises energizing a linear actuator. 9.The method of claim 8, wherein the energizing step comprises operating:a piezoelectric device; or a solenoid; or a magnetostrictive device; ora thermal device; or an electrostatic attractor or repellor; or anoptically energized device.
 10. An optical-modulation method comprisingthe steps of: compression, by a liquid, of a preexisting bubble of gasof a substance different from the liquid; and using relationshipsbetween properties of the liquid and the gas to control lighttransmission along a light path.
 11. The method of claim 10, wherein:the using step comprises controlling the transmission by variation ofreflection at a chamber containing the bubble and liquid.
 12. The methodof claim 11, wherein the chamber is interposed along the path; and: thereflection is used to control transmission across the chamber.
 13. Themethod of claim 11, wherein the variation comprises shifting between:substantially total reflection; and a smaller amount of reflection. 14.The method of claim 13, wherein: the smaller amount of reflection is asubstantially unavoidable level of reflection for the liquid and amaterial of the chamber.
 15. The method of claim 11, wherein: thecompression or expansion step comprises mechanically displacing a volumeof the liquid.
 16. The method of claim 15, wherein: the displacing stepcomprises shifting a diaphragm in contact with the liquid.
 17. Themethod of claim 16, wherein: the shifting step comprises energizing alinear actuator.
 18. The method of claim 17, wherein the energizing stepcomprises operating: a piezoelectric device; or a solenoid; or amagnetostrictive device; or a thermal device; or an electrostaticattractor or repellor; or an optically energized device.
 19. Opticalmodulation apparatus comprising: an exclusively mechanical transducerfor displacing a volume of liquid as between at least two positions; anat least partially mechanical actuator for operating the transducer; andan optical transmission path that intersects the liquid volume when thevolume is in one of the positions, and that does not intersect thevolume when the volume is in another of the positions.
 20. The apparatusof claim 19, wherein: the transducer is neither a thermal nor a chemicalsystem.
 21. The apparatus of claim 19, wherein: the transducer comprisesa movable diaphragm.
 22. The apparatus of claim 21, wherein the actuatoris: a piezoelectric device; or a solenoid; or a magnetostrictive device;or a thermal device; or an electrostatic attractor or repellor.
 23. Theapparatus of claim 21, wherein: the actuator is an optically energizeddevice.
 24. The apparatus of claim 19, wherein: the transducer comprisesa channel containing the liquid volume and having a first cross-section;and a reservoir having a second cross-section that is at least severaltimes the first cross-section, and containing further liquid in apressure-transmitting relationship with the liquid volume.
 25. Theapparatus of claim 19, further comprising: optical structures along thepath for causing the path to use one route when the liquid intersectsthe volume, and another route when the liquid does not intersect thevolume.
 26. The apparatus of claim 24, wherein: the optical structurescomprise a reflective surface whose reflective properties depend uponpresence or absence of the liquid at the surface.
 27. The apparatus ofclaim 26, wherein the reflective properties comprise: conditions forsubstantially total reflection in a first condition of liquid at thesurface; and a smaller level of reflection in a second condition ofliquid at the surface.
 28. Optical modulation apparatus comprising: afluidic transducer having stroke amplification through a ratio ofcross-sections between driving and driven stages; and avariable-reflection optical cell having a control liquid displaced bythe driven stage of the transducer; and an optical transmission pathmodulated by the cell.
 29. The apparatus of claim 28, wherein: thedriven stage comprises a first hydraulic chamber inpressure-transmitting relationship with the control liquid in the cell,and having a first cross-sectional area; and the driving stage comprisesa second hydraulic chamber in pressure-transmitting relationship withthe first hydraulic chamber, and having a second cross-sectional areathat is at least several times the first cross-sectional area.
 30. Theapparatus of claim 29, further comprising: a diaphragm in contact withthe second hydraulic chamber to energize liquid in the driving stage.31. The apparatus of claim 30, further comprising: an actuator operatingthe diaphragm.